A. Field of the Invention
The field of the present invention relates generally to fuel burning stoves and heating systems for heating the interior of a building, such as a home or office. In particular, the present invention relates to fuel burning stoves configured to efficiently and effectively burn pellets, granules or like sized solid heating fuel to provide the desired heating. Even more particularly, the present invention relates to such pellet burning stoves that have gravity feed and natural draft intake systems to provide the fuel and air to the burner.
B. Background
The high cost of heating the interior of a building using conventional, but non-renewable heating fuel sources, such as coal, heating oil, propane and the like, has led many people utilize wood burning fireplaces and stoves as the heat source, particularly for homes, shops and small offices. The basic configuration of wood burning fireplace and stove heating systems has been in use for very many years and has not significantly changed. One of the major disadvantages of standard wood burning fireplaces and stoves is that they are known to be relatively inefficient means of converting the fuel, such as wood logs, into heat. In addition, wood burning fireplaces and stoves are also known to be significant contributors to air pollution. In fact, due to air pollution concerns, many municipalities and counties ban or substantially limit the use of wood burning fireplaces on days when the air quality of the region is such that the air is unable to handle the additional emissions from these sources.
A relatively recent improvement to stove-type heating systems is the pellet burning stove. As well known by those skilled in the art, pellet burning stoves have a number of substantial benefits over the typical wood (i.e., log) burning stove or fireplace, including more efficient burning of the fuel material, less emissions and cleaner emissions. Because of these benefits and benefits with regard to fuel availability, pellet burning stoves have come into wide use. The typical pellet stove utilizes wood pellets that are comprised of by-products from the wood/lumber industry, such as limbs, leaves and other tree waste materials, that are ground, processed and then compressed into relatively small pellet-sized fuel material which are typically held together by a resin or resin-like material. In addition to the obvious benefit of more efficiently utilizing the tree and wood materials, wood pellets are somewhat easier to handle and store than conventional wood logs and the like. Other biomass materials are also known to be utilized for stove pellets. A known disadvantage of pellet fuel, in part due to the resin or other binding material utilized to hold the pellets together, is that it can be somewhat difficult to ignite and require relative high operating temperature for proper or complete combustion of the pellets.
To maintain the temperature required for sustained combustion of the pellet fuel, some pellet stoves utilize electric motor-powered fans or blowers to direct air into the stove's combustion chamber. Some pellet stoves also utilize electrically powered pellet delivery systems, for instance comprising an electric motor driven auger or the like, to direct the pellets into the combustion chamber. As is well known in the industry, the use of electrically powered fans, blowers and pellet delivery systems significantly increase the initial cost, operating cost and complexity of the pellet stove, while providing a less than desirable overall fuel efficiency. In addition, these components are known to have mechanical problems, thereby reducing the reliability of such pellet stoves as a source of heat. The reliability problems of pellet stoves having electrically powered components are compounded when the electrical supply is interrupted due to inclement weather, as happens from time to time because of blizzards or the like, resulting in the pellet stove not being useable when it is most needed. As a result of these known disadvantages, the preferred pellet stoves are those that do not require electrically operated components for combustion or fuel delivery.
Over the years, a number of heating and pellet stoves, and components therefore, have been patented. For instance, U.S. Pat. No. 659,971 to Hower describes a heating stove having a gravity fed combustion chamber that receives fuel from the fuel magazine onto a fire plate that receives draft air from a damper controlled vertical air pipe. U.S. Pat. No. 1,808,487 to Ahlber describes a heating stove or furnace having a gravity fed magazine tube that deposits fuel onto grate bars in the fire box, which receives air from a vent located to the side and below the fire box. U.S. Pat. No. 4,606,282 to Steindal describes a self-feeding wood burning stove configured to automatically feed and burn elongated, round cross-section logs. U.S. Pat. No. 4,989,521 to Traeger, et al. describes a gravity fed pellet burner stove having a hopper that gravity feeds fuel onto an inclined, channel-shaped chute, having holes thereon for air to flow through the fuel, in the burner. An adjustable opening controls the amount of air flowing through the burner.
In an attempt to improve the heating and fuel consumption efficiency of wood burning or pellet stoves, a number of patents describe heating systems that utilize mechanical fuel delivery and forced air apparatuses to deliver fuel and air into the burning chamber. For instance, U.S. Pat. No. 5,893,358 to Whitfield describes a pellet fuel burner having an auger that pushes fuel through a feed conduit onto a burner grate in the firebox, where combustion air is received from a blower through an air manifold. The feed conduit vertically deposits the fuel onto the burner grate. U.S. Pat. No. 6,223,737 to Buckner describes a fuel burning device, configured as a cooking grill, that utilizes an auger to deliver fuel from the hopper to the burner and a blower to provide air for combustion. U.S. Pat. No. 6,336,449 to Drisdelle, et al. describes a solid fuel burner that receives fuel from a hopper by an auger-driven apparatus. Air for the combustion in the burner is provided through a tube and discharged from the burner through a vent by use of an air discharge fan.
Improved natural draft, automatic feed pellet stoves are disclosed in U.S. Pat. Nos. 5,983,885 and 6,397,833 to Jarvi. The stove in these patents stores pellet fuel in a hopper having a discharge slot disposed above one end of a sloped grate. Air for the combustion process is provided to the underside of the grate through an air intake or draft pipe, having a damper thereon, that naturally draws in air from air inlet. The pellets are discharged from the slot onto one end of the sloped grate so that combustion of the fuel takes place as the pellets roll over the grate. Ash from the combustion falls through the grate onto an ash collection pan at the bottom of the firebox.
Although the foregoing patents describe stoves and heaters that are configured to burn pellet fuel, there exists a need for an improved pellet stove that is more efficient at burning pellet fuel and heating the interior of a building. What is needed is pellet stove that is configured to more efficiently burn pellet fuel utilizing natural draft air, thereby eliminating the need for electric blowers and the like to provide combustion air. Additionally, there is a need for such an improved efficiency stove that utilizes a gravity feed system so as to eliminate the necessity of augers or other electrically operated fuel delivery apparatuses. The preferred gravity feed, natural draft pellet stove should effectively and efficiently burn the pellet fuel so as to substantially minimize the amount of particulate matter and other harmful matter in its exhaust emission. In addition to reduced air pollution emissions, the preferred pellet stove will more efficiently provide heat to the interior of the building relative to the amount of fuel consumed thereby. The preferred pellet stove should be able to accomplish the above and be relatively inexpensive to manufacture, simple to operate and comprise few moving components so as to reduce the likelihood of mechanical breakdown.